LABORATORY DIAGNOSIS OF PHEOCHROMOCYTOMA - INFLUENCE OF TECHNOLOGICALIMPROVEMENTS

Laboratory diagnosis of pheochromocytoma must give evidence of increas ed catecholamine production. This requires measurement of catecholamin es and their metabolites (normetanephrine NMN, metanephrine MN and/or VMA) in urine or in plasma. The various assays, can be also performed during dynamic test that stimulate or inhibit catecholamine release. T he recent introduction in biochemistry of high performance liquid chro matography coupled to electrochemical detection (HPLC-ED) has greatly reduced drug-induced interference and has therefore narrowed the refer ence value range. The two groups of compounds that have most benefited from such analytical improvements are urinary metanephrines and VMA. The technical progress has greatly simplified the laboratory diagnosis of pheochromocytoma both by improving the reliability of already avai lable compounds and by favouring the development of news markers. Howe ver, the diagnostic sensitivity of the various urinary and plasmatic m arkers remains very unequal and the diagnosis of pheochromocytoma requ ires a carefully planned sequence of studies including appropriate bio chemical tests able to affirm or to exclude the diagnosis with a high degree of security while reducing the duration and cost of the investi gation. Among urinary markers, metanephrines remain the most direct in dices of catecholamine hypersecretion and provide the most reliable bi ochemical indicators of the existence of pheochromocytoma. The diagnos tic sensitivity of urinary metanephrines (about 98%) greatly exceeds t hat of catecholamines and VMA (60-70%). These differences are related to the diversity and specificity of physiological mechanisms involved in the synthesis, the release and inactivation of markers (catecholami nes, metanephrines, VMA) and to the variety of clinical presentations and secretory patterns of pheochromocytomas.